HEllo, im using JPA (EJB3) for a website where i need to map the relationship between users.

I have the old User class:

- User
+ Long id
+ String name
+ Set<UserRelationship> userRelationships

a UserRelationship class:

- UserRelationship
+ User relatedUser;
+ User relatingUser;
+ int type;

facts:

1) the type can be blocked, friend, awaiting friend approval, denied, so an Enum (Typesafe) could be useful here
2) relatedUser+relatedUser+type should be unique to insure data consistency

3) for a user i need to know:
3.1) which users are blocked
3.2) which users are friends
3.2) which users are awaiting friendship request approval

I have read the docs and tried mapping this several times with no sucess using @ManyToMany, @OneToMany, etc ....

help? ate least a starting point.

thank you

Hi!

I also have basically the same problem with JPA and Hibernate.
I've got a class to store architectural information.

The architecture class has an id, title, description, styleType and additional data that is optional and only added to a additional table if required (formal architecture description).

The architecture styleType can be "general-purpose", "abstract" and "concrete", so I use the Java Enum and "@Enumerated(EnumType.STRING)" as JPA Annotation.
The different architectures are then referencing each other, but it's not a simple "an archicitecture has only one parent". One concreate architecture can be linked as "loose extension" to one general-purpose object and the same concrete architecture can be an "strictly inherited" from another general-purpose object.
It's an m:n referencing object.

Without JPA/Hibernate I would just create two tables, one for the architecture objects and another table for the relationship information.
As a general-purpose style object has no "parent" there will be no entry in the ArchitectureRef table. A style can also not reference itself but that are things that I take care of in my application.

Architectures table columns:
id, title, description and styleType (which is an Enum that can be: "general-purpose", "abstract" and "concrete")

ArchitectureRef table columns:
architectureId, architectureParentId and typeOfReference

TypeOfReference is again an Enum that can be: "strict", "variant", "loose", "builds-upon".

The big question is how to define this in a Java POJO with JPA-Annotations using Hibernate?
Can this be done using "set", "collection",..? If yes, how?


All books and other resources I searched so far do not cover the problem with these referenced objects with more then one parent.
As my problem described above is basically the same problem that josemoreira described I hope someone shows us an example class to do this.

Many thanks in advance.

[Edit1] Fixed some typos

Hello!

I have the same problem as the two guys above.

I want to have a many-to-many relationship on the same table. And also for every link I need an additional column storing some other information. I know from my current experience with Hibernate, that a "middle" table must be created. It should contain two ids pointing to the same table. Also other columns can be added for the additional information. But I am coming short at writing the mapping annotations. The thing which bothers me is that the mapping is to the same table. I could solve the problem if it were two different tables.

I searched a lot on the Internet and couldn't find a solution.

Hope you will help me.

Regards,
Petar